linux-kernel - [PATCH v6 3/5] Drivers: hv: Batch GPA unmap operations to improve large region performance

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Message-ID: 
 <176339836892.27330.9465609709535892557.stgit@skinsburskii-cloud-desktop.internal.cloudapp.net>
Date: Mon, 17 Nov 2025 16:52:48 +0000
From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
To: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v6 3/5] Drivers: hv: Batch GPA unmap operations to improve
 large region performance

Reduce overhead when unmapping large memory regions by batching GPA unmap
operations in 2MB-aligned chunks.

Use a dedicated constant for batch size to improve code clarity and
maintainability.

Signed-off-by: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@...look.com>
Reviewed-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
---
 drivers/hv/mshv_root.h         |    2 ++
 drivers/hv/mshv_root_hv_call.c |    2 +-
 drivers/hv/mshv_root_main.c    |   36 ++++++++++++++++++++++++++++++------
 3 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/drivers/hv/mshv_root.h b/drivers/hv/mshv_root.h
index 3eb815011b46..5eece7077f8b 100644
--- a/drivers/hv/mshv_root.h
+++ b/drivers/hv/mshv_root.h
@@ -32,6 +32,8 @@ static_assert(HV_HYP_PAGE_SIZE == MSHV_HV_PAGE_SIZE);
 
 #define MSHV_PIN_PAGES_BATCH_SIZE	(0x10000000ULL / HV_HYP_PAGE_SIZE)
 
+#define MSHV_MAX_UNMAP_GPA_PAGES	512
+
 struct mshv_vp {
 	u32 vp_index;
 	struct mshv_partition *vp_partition;
diff --git a/drivers/hv/mshv_root_hv_call.c b/drivers/hv/mshv_root_hv_call.c
index caf02cfa49c9..8fa983f1109b 100644
--- a/drivers/hv/mshv_root_hv_call.c
+++ b/drivers/hv/mshv_root_hv_call.c
@@ -17,7 +17,7 @@
 /* Determined empirically */
 #define HV_INIT_PARTITION_DEPOSIT_PAGES 208
 #define HV_MAP_GPA_DEPOSIT_PAGES	256
-#define HV_UMAP_GPA_PAGES		512
+#define HV_UMAP_GPA_PAGES		MSHV_MAX_UNMAP_GPA_PAGES
 
 #define HV_PAGE_COUNT_2M_ALIGNED(pg_count) (!((pg_count) & (0x200 - 1)))
 
diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
index a85872b72b1a..ef36d8115d8a 100644
--- a/drivers/hv/mshv_root_main.c
+++ b/drivers/hv/mshv_root_main.c
@@ -1365,7 +1365,7 @@ mshv_map_user_memory(struct mshv_partition *partition,
 static void mshv_partition_destroy_region(struct mshv_mem_region *region)
 {
 	struct mshv_partition *partition = region->partition;
-	u32 unmap_flags = 0;
+	u64 gfn, gfn_count, start_gfn, end_gfn;
 	int ret;
 
 	hlist_del(&region->hnode);
@@ -1380,12 +1380,36 @@ static void mshv_partition_destroy_region(struct mshv_mem_region *region)
 		}
 	}
 
-	if (region->flags.large_pages)
-		unmap_flags |= HV_UNMAP_GPA_LARGE_PAGE;
+	start_gfn = region->start_gfn;
+	end_gfn = region->start_gfn + region->nr_pages;
+
+	for (gfn = start_gfn; gfn < end_gfn; gfn += gfn_count) {
+		u32 unmap_flags = 0;
+
+		if (gfn % MSHV_MAX_UNMAP_GPA_PAGES)
+			gfn_count = ALIGN(gfn, MSHV_MAX_UNMAP_GPA_PAGES) - gfn;
+		else
+			gfn_count = MSHV_MAX_UNMAP_GPA_PAGES;
+
+		if (gfn + gfn_count > end_gfn)
+			gfn_count = end_gfn - gfn;
 
-	/* ignore unmap failures and continue as process may be exiting */
-	hv_call_unmap_gpa_pages(partition->pt_id, region->start_gfn,
-				region->nr_pages, unmap_flags);
+		/* Skip all pages in this range if none are mapped */
+		if (!memchr_inv(region->pages + (gfn - start_gfn), 0,
+				gfn_count * sizeof(struct page *)))
+			continue;
+
+		if (region->flags.large_pages &&
+		    VALUE_PMD_ALIGNED(gfn) && VALUE_PMD_ALIGNED(gfn_count))
+			unmap_flags |= HV_UNMAP_GPA_LARGE_PAGE;
+
+		ret = hv_call_unmap_gpa_pages(partition->pt_id, gfn,
+					      gfn_count, unmap_flags);
+		if (ret)
+			pt_err(partition,
+			       "Failed to unmap GPA pages %#llx-%#llx: %d\n",
+			       gfn, gfn + gfn_count - 1, ret);
+	}
 
 	mshv_region_invalidate(region);